An electronic device such as a mobile phone uses an antenna module for RFID (Radio Frequency Identification) to mount a near field contactless communication function thereon.
The antenna module performs communication with an antenna coil mounted on a transmitter such as a reader/writer by using inductive coupling. More specifically, in the antenna module, the antenna coil receives a magnetic field from the reader/writer to make it possible to drive an IC that converts the magnetic field into an electric power to function as a communication processing unit.
The antenna module must receive a magnetic flux having a certain value or more from the reader/writer to reliably perform communication. For this purpose, in the antenna module according to the conventional technique, a loop coil is arranged in the housing of the mobile phone to receive a magnetic flux from the reader/writer with the coil.
However, in an antenna module built in an electronic device such as a mobile phone, since magnetic fluxes from the reader/writer are reflected by an eddy current generated when a metal contained in a circuit board in the device or a buttery pack receives a magnetic field from the reader/writer, a smaller number of magnetic fluxes reach the loop coil. In this manner, since the number of magnetic fluxes reaching the loop coil becomes small, the antenna module requires a loop coil having a certain size to collect required magnetic fluxes. Furthermore, the number of magnetic fluxes must be increased by using a magnetic sheet.
As described above, magnetic fluxes from a reader/writer are reflected by an eddy current flowing in a circuit board of an electronic device such as a mobile phone, some magnetic field components face an surface direction of the circuit board are present on a housing source of the electronic device. A coil that receive the components to function as an antenna is proposed in Patent Document 1. More specifically, in Patent Document 1, in order to reduce an occupied area of a coil, an antenna structure obtained by winding a coil on a ferrite core is proposed.